The present invention relates to a process and a device for diagnosing the proper operation of the lamps of hazard lights of a motor vehicle.
All motor vehicles sold at present are fitted with hazard lights. These lights are characterized by the simultaneous and cyclic illuminating of the change of direction indicator lamps (left and right blinkers) of the vehicle.
Such hazard lights are intended to be employed in order to inform vehicles located nearby of a hazard state of the vehicle which could impede the road traffic flow of other users (dangerous parking, breakdown, etc.).
It would appear to be useful to be able to diagnose the proper operation of these lights while they are actually in operation. Indeed, when the driver decides to switch on these hazard lights, it is to inform the other users of a potentially dangerous situation and it is vital that the hazard lights operate correctly so as to carry out the function assigned to them.
Hitherto, only the diagnosis of the proper operation of the blinkers was practiced. Accordingly, it was sufficient to read out the current passing through the circuit powering the blinkers to determine whether a lamp was defective. Indeed, under normal operation, in blinker mode, the left and right pathways are mutually exclusive. Thus, only the left pathway is powered in order to activate the left (front/rear) blinkers; likewise for the right pathway. Therefore, by performing a readout of current forming the sum of the currents passing through the two pathways and by returning the measurement performed solely on the powered pathway, one automatically determines on which side the inoperative lamp is located. This information is then forwarded to the driver by causing the blinker pilot situated on the dashboard and corresponding to the side exhibiting a detective lamp to blink more rapidly. Thus, a defective lamp detected on the left side causes a doubling of the frequency of blinking of the left pilot.
The diagnosis of the proper operation of the lamps of the hazard lights necessarily involving that of the blinker lamps, it would appear to be opportune to utilize the diagnosis of the blinkers in order to diagnose the hazard lights. Indeed, this makes it possible to dispense with any additional device. Unfortunately, since the diagnosis of the blinkers effects a simple readout of the current flowing through the two pathways, and since these two pathways are powered simultaneously (in the case of the hazard lights), it is impossible simply to use the diagnosis of the blinker function to diagnose the hazard lights. Indeed, in this case, it is no longer possible to determine the side exhibiting a defective lamp, and still more serious, the variations in internal resistance which are due to the cyclic powering of all the lamps are greater than those caused by a defective lamp. Therefore, it is not possible to use the device for diagnosing the blinkers to diagnose the hazard lights.
The aim of the present invention is to diagnose the hazard lights according to a process and a device which are as similar as possible to those used for the diagnosis of the blinkers.
Accordingly, the present invention relates to a process for diagnosing the proper operation of the lamps of hazard lights of a motor vehicle, said process being one which consists in:
temporally and alternately shifting the end of illumination of the right and left change of direction indicator lamps of the vehicle,
measuring the current passing through the power circuit of said hazard lamps during the temporal shift,
comparing the measured value with a reference value, and
deducing therefrom whether at least one of the lamps is inoperative and in this case informing the driver thereof.
The shifting of the end of illumination of the right and left indicator lamps makes it possible to perform the measurement of the current flowing inside the circuit solely for the time when only one of the sides is powered. Therefore, it is possible, when a defective lamp is detected, to signal which side of the vehicle this defective lamp is located on. Moreover, by performing this measurement of the current while some of the indicator lamps are powered (one side only) and only at the end of illumination of the lamps (that is to say when the current has stabilized at a low level inside the lamp), it is possible to avoid the variations in resistance of the lamps due to the inrush current at the start of illumination and, therefore, the measured variations in current are directly representative here of a defective lamp.
It will be observed that the alternate temporal shifting of the end of illumination makes it possible, during a first measurement, to determine the current flowing in the lamps situated on one side of the vehicle and, during the following measurement, to determine the current flowing in the lamps situated on the other side of the vehicle.
Of course, the temporal shift of the end of illumination of the lamps remains invisible to the naked eye. Therefore, the right and left blinkers light up at the same time and seem to go out at the same time (for an observer of the vehicle) whereas in fact they do indeed light up at the same time but go out one after the other.
To prevent the temporal shift from being perceptible to the eye, it is preferable for this shift to remain less than 50 ms. Preferably, it is of the order of 15 ms.
Advantageously, this alternate temporal shift and the measurement of the current passing through the lamps are performed continuously. Permanent diagnosis of the proper operation of the lamps of the hazard lights is thus achieved.
The present invention also relates to a corresponding diagnostic device.